1. Field of the Invention
The present invention relates to a light integration apparatus for use in a projection device, and more particularly, to a light integration apparatus that utilizes integration rods to integrate multiple light sources.
2. Descriptions of the Related Art
Currently, projection devices are widely used in offices, houses, conference rooms and places of the like. A projection device generally includes a light source, a prism, a color wheel, an imaging lens and other optical components. Before being projected, light emitted from the light source is integrated by an integration rod and then travels into the color wheel and the imaging lens. Accordingly, the arrangement and design of the integration rod have become a key technology in the projection device.
Among various types of projection devices, the digital light processing (DLP) projection device is capable of receiving a digital signal and generating a sequence of digital light pulses. The internal arrangement of a conventional DLP projection device 1 is shown in FIG. 1. The projection device 1 includes a light source 11, an integration rod 12, a color wheel 13, a light coupling device 14, a digital micromirror device (DMD) 15 and a lens 16. FIG. 1 simply shows a single-chip DMD 15 and a single light source 11 for purpose of illustration, and the light source 11 is preferred to be an ultra-high pressure (UHP) lamp, because the ultra-high pressure (UHP) lamp has the advantages of low cost and high light emission efficiency. In the arrangement shown in FIG. 1, the color wheel 13 is used for filtering the light emitted from the light source 11 into three primary colors. Specifically, after the light passes through the integration rod 12, a preliminary imaging takes place and, through the color wheel 13 that disposed at the back end of the integration rod 12, the light of the three primary colors are selectively generated. Subsequently, the light enters the light coupling device 14 and is reflected by various micromirror structures of the DMD 15 in a controllable manner before being projected from the lens 16.
An illumination structure with multiple light sources integrated therein is considered in the prior art to improve light intensity. FIG. 2A shows such an illumination structure with two light sources integrated therein. In this structure, light emitted from the first light source 211 and light emitted from the second light source 212 are integrated in a prism 221 before entering the integration rod 223. As shown, the light emitted from the first light source 211 is internally reflected by the prism 221, while the light emitted from the second light source 212 is internally refracted in the prism 221, so that the light emitted from the first light source 211 and the second light source 212 are integrated and then be projected in the same direction. The first light source 211 and the second light source 212 can be placed at different locations according to the internal arrangement of the projection device, and the light emitted from the first light source 211 and the light emitted from the second light source 212 can be integrated into a uniform light source with a size suited to the DMD.
Another conventional illumination structure with four light sources integrated therein is shown in FIG. 2B. The first light source 211, the second light source 212, the third light source 213 and the fourth light source 214 are disposed horizontally in the projection device. More specifically, the first light source 211 and the second light source 212 are disposed opposite to each other at both sides of a first reflecting prism 231 and a first integration rod 241, and light therefrom is reflected by the first reflecting prism 231 towards the longitudinal direction of the first integration rod 241 to be integrated therein. Similarly, the third light source 213 and the fourth light source 214 are disposed opposite to each other on both sides of the second reflecting prism 232 and second integration rod 242, and light therefrom is reflected by the second reflecting prism 232 towards the longitudinal direction of the second integration rod 242 to be integrated therein. Finally, all the light enters a third integration rod 243 and is integrated into a uniform light source with a size suited to the DMD.
However, the conventional illumination structures have a number of drawbacks. First, in each of the above arrangements, an integration rod for integrating light (e.g. the integration rod 223 or the third integration rod 243 described above) has to be disposed at the back end for eliminating the dark lines due to the prism boundaries at the front end and integrating light from different light sources into a single light source with a size suited to the DMD. Conceivably, the more integration rods or optical components that are used in the light integration process, the more light will be lost and the assembling of the projection device will be more complicated.
Furthermore, the conventional arrangement of the light sources described above presents the difficulty in heat dissipation management. Because for lowering the high temperature of the bulbs of the light sources, a plurality of cooling fans have to be disposed adjacent to the bulbs of the light sources respectively, and a fan disposed for guiding hot air out of the projection device is also necessary. However, in the conventional illumination structure shown in FIG. 2B, all the light sources are disposed at the same horizontal level, which makes it relatively difficult to arrange a number of fans and is also unfavorable for arrangement of elements within the projection device. Consequently, unsmooth air circulation occurs and brings about poor heat dissipation, high operation temperature and short life-span of the bulbs. Moreover, disposing the light sources on the same horizontal level makes it difficult to replace light sources, so that the maintenance cost is increased.